The preparation of cereal for grinding more particularly for high-grinding, comprises a plurality of method steps:
the screening out of sand and clods, PA1 the sorting out of various foreign particles, for example stones, seeds, and husk fragments, PA1 the removal of adhering dirt, PA1 moistening of the cereal from storage moisture (e.g. 10-12%) to grinding moisture (to over 15% water content), PA1 conditioning the cereal for 12 to 48 hours, PA1 possibly also a scouring or peeling of individual skin parts, or the whole grain skin. PA1 removal of all foreign seeds, PA1 removal of all impurities and skin pieces, PA1 reduction of bacteriological impurities, PA1 obtaining an intact grain.
The cereal grain has basically a threefold skin structure. The outermost skin consists of outer layer, longitudinal cells, transverse cells and tubular cells, which make up about 5.5% of the entire grain. There follows a central double layer, the so-called colour layer as well as a colourless layer, taking up about 2.5% of the grain. The innermost layer amounts to 7% of the grain weight, and is called the aleurone layer. There remain the embryo or germ, with 2.5%, and the large remaining part the endosperm which amounts to about 82.5% of the entire grain. A known problem area in the production of wholemeal, brown and white flours, also middlings and semolina, involves the germ, since the germ has a high fat content. The germ is a valuable component, and is suitable for example for the extraction of oil. But it is the fat which in the broken-open state of the germ limits the keeping qualities of the milling products especially when there is a considerable germ fraction. The miller aims to remove all germ in the milling process with as little damage as possible. Therefore, the cereal grain is to be conducted along with the germ as far as possible without damage up to the first grinding stage.
The recent past has been marked by two tendencies. Firstly by reducing, for economic reasons, the number of machines or apparatus for the cleaning stage or preparation for milling. The aim was in the direction of using just dry sorting machines, wetting of the cereal, and as small conditioning cells as possible. According to the second tendency it has been proposed, quite the opposite, to peel and polish the milling cereal through many stages to almost the endosperm, similarly to what happens in rice milling.
For example according to DE-PS No. 1 164 210 it was proposed to remove the outermost layers completely. Depending on the type of cereal 3.2-5.7%, i.e. to some degree the entire outer skin formation, is taken off by repeated moistening, stripping and sifting. The removal of such large skin fractions has to be prepared and accompanied by carefully controlled and repeated treatment of the grain, wherein in addition to the moisture, heat has also been applied over a sufficient influence time, with moderate movement.
The applicant company itself, according to CH-PS No. 640 750, proposed so to speak a middle road of peeling off 6-10% of the grain, or 50-60% of the grain skin, be-before grinding. For this, four successive method steps are proposed: dry cleaning--moist peeling--intensive wetting--roller grinding. But for economic or viable-operation reasons that method was un-successful as regards becoming established in actual practice.
In a still earlier proposed solution according to GB-PS No. 1 258 230, to increase the yield, the various skins are repeated "batchwise" treatment. Although this complete-peeling method has now been known for over two decades, it has not become established in actual practice.
In recent times it has again been attempted, according to U.S. Pat. No. 5,025,993, to carry out some of the operations of the usual milling process within the preparation-for-milling stage by a systematic and repeated total scouring and peeling. But very extensively arranged practical tests showed no advantages, at least as regards the overall economy. On the contrary, in the case of complete grain peeling, very moist skin fractions are produced which have to be separately treated and in part dried. Most of the tests gave no higher yield of white flours and semolinas. The outlay for the milling process per se cannot be substantially reduced this way. The U.S. Pat. No. 5,025,993 is based on what happens in peeling and polishing practice in the milling of rice. The actual disadvantage is that each individual machine has only a very small throughput, so that a large number of individual machines is needed in the case of high outputs of e.g. 20-40 t/h.